In this report, gaseous toluene biodegradation results in a flat composite membrane reactor inoculated with Pseudomonas putida TVA8 are presented. Preliminary abiotic experiments showed that transport of toluene through the membrane was linearly and negatively correlated with the gas residence time (tau). During a 339-day biofiltration experiment, the influence of gas residence time (2 - 24 sec) and mass loading rate (B-v; 10 - 483 g m(-3) h(-1)) on the toluene elimination capacity was investigated. A maximum elimination capacity (ECmax) of 397 g m(-3) h(-1) was achieved at tau = 24 sec and B-v = 473 g m(-3) h(-1). Expressed per unit membrane area, the ECm,max was 0.793 g m(-2) h(-1), which is five times higher than results obtained with other membrane bioreactor experiments in the same range of loading rates. At low gas residence times, reactor performance was limited by mass transfer. Toluene concentration profiles along the membrane were measured for several biotic and abiotic conditions. For inlet concentrations (C-in) UP to 1 g m(-3), more than 90% was eliminated 3 at 15 cm from the reactor inlet. For C-in > 1.65 g m(-3), longer membranes are necessary to obtain these high removal efficiencies. (C) 2004 Wiley Periodicals, Inc.